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Re: CR of lights (CRI)

> Date: Thu, 17 Jan 2002 13:23:33 -0800
> From: "Roxanne Bittman" <rbittman at dfg_ca.gov>
> Subject: CR of lights
> At one time, I tried out a number of different fluorescent bulbs with different Kelvin ratings and CR ratings to find what
> looked best to me.  I agree with Michael Rubin that 6500 or 6700 is just about perfect since it looks most "white."  In
> reality it is quite blue, but our eyes don't perceive it that way.  The 5000K bulbs look too yellow to me.

The general color often depends on the context in which they are seen. The CRI
(Color Rendition Index) is a measure of how "white" the light appears to a
standard observer. Below 80 is fairly noticeable tinting and above 85 or so
looks pretty white. The tinting can be any color, but is often purplish, pink,
yellow, etc. (anything but white).

5000K is the color of daytime sunlight, while 6500 is like daylight in shade,
where the blue skylight tends to dominate more. Old B&W TVs used to look
startlingly blue when glimpsed through an open window, because they used a
phosphor standard that was about 8600K.

The old TVs "looked white" but that was because they were the dominant light
being seen when you were in the room watching them. Our brain does a wonderful
job of adjusting for different illuminations. For planted tanks, I prefer
5000K or even 4000K tubes as they provide more of the photosynthetically
active red part of the spectrum (all other things being equal). Our brain
makes the result look OK, IMO, if the CRI is well above 80, *and* the room
illumination doesn't fight with the tank lights. YMMV, as it is a *very*
subjective thing. 

You can change the apparent color of a tank dramatically, by simply changing
the surrounding room illumination. Try it sometime. You may be startled.


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